How can this be??

[Popajama]

After several weeks of sub zero weather we had a day of above freezing temperatures. The next morning several homes in my area experienced frozen water supply lines. Old timers just grin and say, "Yep, a thaw will push the frost down".
This flys in the face of logic to me but you cannot dispute the fact that it happens and that the ocurrance is no surprise to the old timers who claim they have witnessed it for years. Let me add that the supply lines are buried below the safe frost line but this has been an unusually cold winter here in New Brunswick, Canada.

Can anyone enlighten me as to how a "Thaw will push the frost down"?

This is driving me nuts.

Popajama

[scotth]

When you say, "The next morning several homes in my area experienced frozen water supply lines."

Do you mean that they began leaking the next morning due to rupture, or...

Do you mean that water was being delivered to the other end of the pipe until the next morning and then quit?

If you mean the first, the explanation could be that the pipes were frozen hard for several days and then thawed and started leaking/spraying.

[pupdog]

This is speculation, but testable...

Soil moisture migrates in cold weather, forming ice lenses (this much is known by soils engineers). My guess is, a thaw allows water from the ice lenses to melt & percolate downward, where it can freeze during a subsequent temperature drop. But somehow I suspect that the pipes freeze & the frost is "pushed down" because, despite a brief thaw, the prolonged cold weather allows ever-deeper soil regions to lose heat (of course, the "cold" is not really moving down!).

[Popajama]

Originally posted by scotth
When you say, "The next morning several homes in my area experienced frozen water supply lines."

Do you mean that they began leaking the next morning due to rupture, or...

Do you mean that water was being delivered to the other end of the pipe until the next morning and then quit?

If you mean the first, the explanation could be that the pipes were frozen hard for several days and then thawed and started leaking/spraying.

I mean the second. In the evening everything normal. Next morning..no water. No rupture and spraying.

Also it was hardly a thaw. Just a day of above freezing with little visable widespread melting.

Not only are the pipes buried deeply in the ground but are covered with several feet of snow except where they pass under the roadway which is of course kept clear of snow. I suspect this is where they are frozen because they lack the insulation the snow provides.

To my way of thinking the rise to above freezing temperature should halt the downward advancement of frost not accelerate it.

I know there is a lot of smart people in this forum. Give me your thoughts.

Cheers

Popajama

Cheers

[fishbob]

It could be that it takes several weeks plus for the freeze depth to reach the pipes. Also there is a time lag between warmer temps at the surface and the start of warming at depth - sometimes weeks. It could also be that your cold spells usually only last several weeks and therefore, the pipes don't freeze until after the cold weather has past.

[garys_2k]

It is absolutely true that heat flow takes time. The "cold" can take weeks to migrate deep enough to reach pipes, and a brief warm spell at the surface will likewise take weeks to migrate through the recently-chilled soil.

I suspect the reason the old-timers believe this expression is because of this time lag, it often is already past the peak of cold weather, when occasional warm spells or a general warmup is underway, by the time the core of the cold (heat depletion zone) reaches its maximum depth.

After the weather consistently warms up you have heat entering from the top, so the soil begins to increase in temperature there, as well as from the bottom. The zone of sub-freezing soil starts to shrink.

[kittynh]

So, does any of this explain frost heaves???

when I moved here I saw a hand lettered sign saying ,"Frost Heaves" and I was like ,"vomiting frost?", then I went airborne in my car. It always seems to happen after a thaw, but I know that with the temp drop everything freezes at night. So I think it has something to do with melting and refreezing.

[fishbob]

Frost heaves (the non-vomiting kind) are related to water content. Soil that drains well (sand and gravel) is less susceptable to heaving, soil that retains water (clay and silt) is more susceptable.